I agree with getting some help to learn to ride this horse effectively. With a cue like that, it is so easy to screw it up and end up with some really big problems.
I took a mare in for training that had 30 days under another trainer. Every time she got pissy or stubborn or even just a little bit spooked, she would start running backward and you couldn't stop her. If you used your legs, she would just go faster, if you whopped her on the butt, she would go faster still.
It took quite a few "come to jesus" meetings and her nearly falling on me several times before she finally started to get over it.